Extraction process



Sept. 27, 1938. A ANDERSON 2,131,422

EXTRACTION PROCES S Filed Feb. 20, 1937 Salve/7f Propane /nvcr7/0r:A/v/nR linderson By his A/f0rneg;

Patented Sept. 27, 1938 EXTRACTION PROCESS Alvin P. Anderson, Alton,IlL, assignor to Shell Development Company, San'Francisco, Calii'., acorporation of Delaware Application February 20, 1937, Serial No.126,889

10 Claims. (Cl. 196-13) This invention relates to a' process for thetreatment of hydrocarbon oils, such as petroleum fractions, withselective solvents comprising cresylic acid, and is particularly usefulin the extraction of higher-boiling residual or distillate oils, such ascylinder oil, lubricating distillates, spindle oil, transformer oil, butmay be applied also to the treatment of lower boiling fractions.

The types of hydrocarbons occurring in petroleum fractions and theirrelative concentration vary with the source and the boiling range of thefraction, and these variations in initial composition, as well as thequality of the desired extraction product, determine the exact nature ofthe separation eflected in the extraction processes. In general,however, the purpose of the process is to dissolve those components ofthe initial oil which are more aromatic, naphthenic, and/or olefinic innature, i. e., those which have a relatively lower hydrogen-carbonratio, while leav-v ing undissolved the relatively more parafliniccomponents. In the case of lubricating oils, the more paraffiniohydrocarbons present in crude lubricating oil fractions are moredesirable because, as compared with themore soluble hydrocarbons, theirviscosity is not so greatly affected by changes in temperature, arechemically more inert and stable, and exhibit less tendency towards theformation of undesirable resinous or sludge forming constituents oncontact with air at elevated temperatures. This group of hydrocarbons,in the case of lubricating oils, does not include those compoundsusually designated as wax" or petrolatum.

As a matter of convenience hereafter the component or group ofcomponents of the initial oil which it is desired to remove in theextraction process by preferential dissolution in the selective solventas the extract will be designated as non-paraflinic constituents, andthe component or group of components which it is desired to recover asthe raftinate will be designated as paraffinic, it being understood thatthese terms are relative, and are to be interpreted with regard to thecomposition of the initial material and the extraction productsproduced, the non-paraffinic portion being in each case more readilysoluble in the extract phase than the paraflinic portion.

According to one mode of carrying out such an extraction process, aselective solvent consisting of cresylic acid, or of a mixture ofcresylic acid with a similar second solvent, such as phenol, is passedthrough a packed tower or a multi-stage treater countercurrently to anauxiliary solvent which is at least partially immiscible with theselective solvent in the presence of the oil, and the oil is subjectedto the extracting action of these countercurrent streams by introducingit into the system either with the auxiliary solvent, or at a pointintermediate to the points of introduction of the selective andauxiliary solvents respectively. Such a process is described in theTuttle Patent No. 1,912,349. In certain processes the auxiliary solventis introduced into the system at a plurality of points, as, for example,near the point of removal of the extract, at the point of introductionof the oil, and at a point lying between the points of introduction ofthe oil and the selective solvent, respectively.

Particularly useful as auxiliary solvents in such a process are liquidor liquefied hydrocarbon distillates boiling below about 45 0., althoughhigher. boiling preferably 1 aromatic-free distillates I may beemployed. Propane, either alone, or in process of the type describedabove, involving the flow of an oil and an auxiliary solventcountercurrently to a selective solventcomprising cresylic acid throughseveral stages (which stages may be either real, as when a series ofinterconnected mixers and settlers or centrifuges is provided, orvirtual, as when using one or more packed towers), the maximum rate ofthroughput of the oil is often undesirably limited by the slow orincomplete separation of the phases in one or more stages. Thus, whenfeeding too much of the initial oil into the system, whether or not therate of flow of selective solvent is varied, the mixture in one or morestages becomes cloudy or emulsified, causing some of the extract phaseto move in the wrong direction by being intermixed with the rafllnate;as a result the sharpness of the separation is lowered as indicated, forexample, by a decrease in theviscosity index or paraflinicity of theraillnate oil,and anincrease in that of the extract oil, due toentrainment of railinate in the extract. This condition may progress sofar as eventually to result in the coalescence of the two phases, withthe result that the extraction zone is flooded with a solution of oiland solvents and the extraction ceases.

According to the present invention it was found thatthe speed ofseparation of the phases, whether effected in a settling tank, in acentrifuge, or in a tower, can be materially increased by employing,instead of anhydrous selective solvent, a mixture of a cresylicacid-containing selective solvent and a small amount of water. It wasfound that, when extracting viscous residual oils, at least 0.3% ofwater are necessary to effect an improvement in the settling rates, andthat for safe uniform operation the water content should be maintainedat above 0.4% by weight,

based on the selective solvent, while the best operation occurs when thewater content is kept within the range from 0.5 to 0.7%. Other watermiscible low-molecular oxygenated organic compounds, such as methylalcohol, glycerol, glycol, acetone, etc., may be employed in place of ortogether with water to improve the settling rates. When such compoundsare employed in addition to water, the quantity of water -may be as lowas 0.2%.

It has, moreover, been found that it is essential that the waterconcentration be maintained below 1.0% and, preferably, below 0.8%. Whenmore than this amount of water is employed, there is a decided shift inthe solubility equilibria toward increases in the sizes of the raflinatelayers, and towards decreased oil concentrations in the extract phases,causing larger quantities of hydrocarbons of intermediate solubility tobe dissolved in the raillnate phase, thereby lowering the quality of theultimate raflinate. Such a shift in equilibria upsets the extractionprocess and prevents the production of a raflinate of the desiredquality in an apparatus of a fixed number of real or virtual stages.While it is sometimes possible partially to restore the equilibria byincreasing the temperature, this is undesirable because an increase intemperature was found to cause slower rates of partition between thephases.

It should be noted that the water or other material is, in the presentprocess, added merely to improve the rate of settling, the amountpresent in the system being insuflicient to cause a substantial loweringof the solvent power of the selective solvent for oil. Thisdistinguishes the present invention from prior processes in which suchsubstances have been employed in larger concentrations with the purposeof regulating the solvent power of the selective solvent. Thus,according to the present invention the quantity of water or other polaragent is sufllciently small not to cause the oil concentration in theextract phase in the stage at which the fresh solvent is introduced tobe lowered by more than about 20%, as compared to and based on theconcentration of oil in the corresponding extract phase when anhydrousselective solvent is employed.

The present invention, therefore, is based upon the discovery that thereis a critical range of concentrations of water which materially improvesthe rate of separation of the rafiinate phase from the extract phasewithout causing so great a shift in the solubility equilibria as toupset the extraction process.

While the addition of small amounts of water is especially useful inextraction processes employing propane as the auxiliary solvent, otherequivalent auxiliary solvents, as outlined above, may also be employed.The addition of water in rocesses operating without auxiliary solventsis,

however, undesirable because it was found that in the absence of anauxiliary solvent even the small quantities of water employed in thepresent process are detrimental to the selectivity of cresylic acid.

The expression cresylic acid, as employed in the present specificationand claims, is intended to include o-, m-, and p-hydroxy toluene,mixtures of two or more of these as well as mixtures containing theirhigher homologues, such as ethyl hydroxy benzenes. The expression"cresylic acidcontaining, as applied to selective solvents, is intendedto designate a selective solvent which may, save for the small amount ofwater specified according to the present invention, consist entirely ofcresylic acid, as defined above, as well as selective solventscontaining quantities (not over 65% by weight) of other aromatic andparticularly phenolic solvents, such as phenol. By way of example,excellent results have been obtained by employing 0.6% of water in anextraction process employing as the selective solvent a mixture of 70%cresylic acid and 30% of phenol. It was, moreover, found that thesettling rate can be increased by using a selective solvent whichcontains a concentration of phenol higher.

' ing water, described below, was found to be particularly useful inthat it also improved the separation of dissolved solvent from theraflinate phase.

The process may, for example, be operated in an apparatus of the typeillustrated schematically in the drawing, which is a flow diagram of oneembodiment of the present invention. In the drawing, A and B representcylindrical shells, filled with a plurality of partitions so as toprovide settling chambers or stages I to 8. Each stage is equipped witha mixing device Ia. to 8a, which may be provided with means fordistributing a liquid mixture or emulsion into the chambers with aminimum of turbulence. The chambers are interconnected by conduits, asshown.

Cresylic acid enters mixer 8a from tank 9 via line H) by the action ofpump 8e through valve l2. An auxiliary solvent, like propane, is fedinto mixer la from storage tank l3 via line H, controlled by valve l5.Raw oil, such as a topped crude, is introduced into one of theintermediate stages, such as, for example, stage 3 from tank i6 via lineI! and pump l8, at a rate controlled by valve l9.

As aresult of feeding the cresylic acid solvent, propane, and initialoil into mixers 8a, Ia, and 3a, respectively, the cresylic acid solventand propane flow countercurrently to one another through the severalsections in the following manner: The phase discharged from each of themixers stratifies in the chambers l to 8 to form relatively lighterraflinate phases and relatively heavier extract phases. The extractphases settle and are withdrawn via lines lc to 80, while the rafiinatephases are withdrawn via lines Id to 8d. Extract phases from stages 2 to8 are fed into mixers la to la, respectively, by pumps le to la, andraifinate phases from stages I to I are fed into mixers 2a to 8a,respectively, via valves U to 8!. The ultimate rafllnate phase iswithdrawn through valve 20, and may be treated for the recovery of thepropane and cresylic acid solvent in any desired manner. The ultimateextract phase is withdrawn through a valve 2| in line lc for a similartreatment.

The improvement according to the present invention resides in employingin the settling chambers a cresylic acid solvent containing smallquantities of water, as described above. The solvent in the tank 9 maycontain this water. When this solvent is anhydrous or substantially so,water may be introduced at one or more points in the process, as, forexample, into the line l through a valve 22.

Instead of adding all of the water through the valve 22, I prefer to addthe major portion of the water used in accordance with this invention tothe ultimate rafilnate phase withdrawn from the chamber 8, either beforeor after this phase is freed of the auxiliary solvent. Thus, theraflinate phase may be flowed through a flashing stage 23' whereinpropane is separated and withdrawn at 24. The residual portion of theramnate phase is mixed with water fed via the valve 25, and theresulting mixture is stratified in settling tank 26. The addition ofwater causes separation of the mixture into two secondary liquid phases:one consists of a substantially oil-free concentrated aqueous solutionof cresylic acid, which is withdrawn at the bottom and combined withsubstan-' tially anhydrous cresylic acid from the tank 9 via the line 2!and the valve 28; the other consists substantially of the refinedrafilnate oil containing a very small amount of cresylic acid, and maybe withdrawn at 29. The latter phase may be further treated, forinstance, by vacuum distillation, to recover a solvent-free oilraflinate. The anhydrous cresylic acid in the tank 9 may be either thefresh make-up solvent or that recovered by distillation or by some othermethodv from the extract phase produced in the same process. Theproportions in which the anhydrous solvent and its aqueous solution arecombined, either prior to or after being introduced into the extractionzone, are regulated to produce a solvent containing the desiredconcentration of water within the above specified range. Following is anillustrative example of this preferred form of the process:

The raifinate phase produced by a continuous method of countercurrentextraction in which initial oil was introduced at an intermediate pointinto counterflowing .streams of propane and cresylic acid was foundto',contain about 16% of the total cresylic acid used in the process. Itwas subjected to the following treatment to separate the bulk ofcresylic acid from the oil: propane was flashed off by reducing thepressure on the rafiinate phase. A small quantity of water (about 3%based on cresylic acid in this phase) was then added to the residualportion of the rafiinate phase, whereupon the oil-cresylic acid solutionseparated into an oil layer and an aqueous cresylic acid layer. Theaddition of such a large amount of water greatly improved the speed ofseparation between the oil and acid layers, as compared to priorprocesses in which small amounts of water (about 1%) were added. Thelayers were separated and the aqueous cresylic acid was combined with ananhydrous cresylic acid forming an aqueous cresylic acid solution withwater content of about .6%; this solution was reused in the extractionof additional quantities of oil.

The degree of improvement obtainable by the addition of water may beseen from the following data. Employing a solvent mixture containing 30%phenol and 70% cresylic acid in a double countercurrent extractionsystem, a combination with. propane as the-auxiliary solvent, for theextraction of a residual oil having an initial viscosity index between60 and '72, the phases withdrawn from the extraction stage nearest thepoint of introduction of the solvent were flowed through an eductor tubeat the rate of 17 feet per second, .and the rate of settling determinedby flowing the mixture through a 24 inch long gauge glass bomb. Withoutwater the average rate of settling was about 0.3 foot per second, whichwas increased to 0.83 foot per second when 0.8% of water were added,employing the same temperature.

I claim as my invention:

1. A process for the separation of parafi'lni'c and non-paramnioportions of a petroleum lubricating oil fraction containing the same,comprising the steps of flowing concurrent streams of said oil and aliquid auxiliary solvent for the parafiinic portion of the oil,consisting predominantly of one or more liquid or liquefied hydrocarbonscontaining lessthan six carbon atoms in the molecule through anextraction zone counter-currently to a stream of a cresylicacid-containing selective solvent containing between about 0.3% and 1.0%water under conditions to cause the formation of counterfiowingrafflnate and extract phases, separating said phases, and removing theseparated phases at spaced points in the extraction zone.

2. The process according to claim 1 in which the water concentration inthe selective solvent is between about 0.5 and 0.7%.

3. The process according to claim 1 in which the auxiliary solventconsists predominantly of propane.

4. The process according to claim 1 in which the liquid phases areseparated by settling.

5. A process for 'the separation of paraflinic and non-parafllnicportions of hydrocarbon oil containing the same which comprises flowingsaid oil through an extraction zone countercurrently to -a cresylicacid-containing selective solvent containing between about 0.3% and 1.0%water in the presence of a liquid auxiliary solvent for the paraifinicportion of the oil which, when mixed with said selective solvent in thepresence of the oil, is capable of forming two liquid phases, therebyproducing liquid extract and rafllnate phases, separating said phasesand withdrawing the separated phases at difierent points in theextraction zone.

6. A continuous process for the separation of parafiinic andnon-paraflinic portions of hydrocarbon oil containing the same, whichcomprises continuously flowing said oil through a countercurrentextraction apparatus countercurrently to a cresylic-acid containingselective solvent in the presence of a liquid auxiliary solvent forparafiinic portions of the oil which, when mixed with said selectivesolvent in the presence of the oil is capable of causing the formationofliquid raftinate and extract phases, continuously separating andwithdrawing raffinate and extract phases from said apparatus at spacedpoints thereof, adding a quantity of water to the withdrawn rafiinatephase to cause the formation of a liquid aqueous solvent phase and aliquid oil phase, separating said aqueous solvent phase from the oilphase, mixing said separated aqueous solvent with substantiallyanhydrous cresylic acidcontaining selective solvent, and continuouslyintroducing the resulting mixture of anhydrous and aqueous solvents intothe apparatus for the extraction of oil, said quantity 01' water beingsuch as to cause said resulting mixture of anhydrous and aqueoussolvents to have a water concentration of between 0.3% and 1.0%.

'7. The process according to claim 6 in which the said quantity of wateris such that the water concentration in said resulting mixture ofanhydrous and aqueous solvents is between about 0.5% and 0.7%.

8. A process for the separation of parafllnic and non-parafilnicportions of hydrocarbon 011 containing the same which comprisescontacting said oil with a cresylic acid-containing selective solventcontaining between about 0.3% and 1.0% of a separating aid of the classconsisting of water, methyl alcohol, glycerol, and glycol in thepresence of a liquid auxiliary solvent for the parafflnic portion of theoil which, when mixed with said selective solvent in the presence of theoil, is capable of forming two liquid phases, and separating saidphases.

9. A process for the separation of parafllnic and non-parafllnicportions of hydrocarbon oil containing the same which comprisescontacting said oil with a cresylic acid-containing selective solventcontaining between 0.2% and 1.0% of water and in addition a smallquantity of a low molecular oxygenated water-miscible organic compoundin the presence of a liquid auxiliary solvent for the parafllnic portionof the oil which, when mixed with said selective solvent in the presenceof the oil, is capable of forming two liquid phases, and separating saidphases.

10. A process for the separation of parafflnic and non-paramnic portionsof hydrocarbon 011 containing the same which comprises contacting saidoil with a cresylic acid-containing selective solvent containing betweenabout 0.3% and 1.0% of a separating aid of the class consisting ofwater, methyl alcohol, glycerol, and glycol in the presence of a liquidauxiliary solvent consisting predominantly of hydrocarbons normallyboiling below C. which, when mixed with said selective solvent in thepresence of the oil, is capable of forming two liquid phases, andseparating said phases.

ALVIN P. ANDERSON.

